The invention relates to a powder metering apparatus comprising a metering chamber which defines a powder metering volume and can be emptied through an outlet opening, wherein, in order to draw in powder from a powder supply line, a negative pressure can be applied to the metering chamber through a diaphragm which bounds the metering chamber.
The invention further relates to a powder metering method for operating a powder metering apparatus constructed according to the concept of the invention, wherein powder is drawn in by means of negative pressure into a metering chamber delimited by a diaphragm and having an outlet opening.
From the applicant's EP 0 937 004 B2 an apparatus and a method are known for the pneumatic conveying of powder, wherein the apparatus has a cylindrical chamber into which powder is able to be drawn in from a powder supply line by means of negative pressure, wherein the metering chamber is supplied with negative pressure through the diaphragm. The fixedly arranged diaphragm has the task here of preventing powder from being drawn into the negative pressure line. The chamber is not completely filled with powder here before the emptying in the drawing-in phase. The known apparatus concerns a transportation apparatus with a predetermined chamber volume, in which the drawn-in powder is emptied exclusively via an application of the chamber by compressed air through a lower outlet opening. In particular if the drawing-in time for the powder was selected to be very long and consequently the powder was intensively compacted in the chamber, difficulties were to be expected on emptying the chamber.
From the applicant's EP 0 789 230 B1 a metering apparatus of complex construction is known for the metering of powders, in which the metering volume is able to be set.
A powder metering apparatus with a flexible diaphragm arranged in a suspended manner is described in U.S. Pat. No. 3,391,963. The diaphragm is arrested at a piston, which together with the diaphragm is axially adjusted during filling of the pump chamber with powder. During emptying of the chamber, an adjustment takes place in the opposite direction, and a resulting stroke makes provision that powder adhering to the diaphragm is shaken off.
Further powder metering apparatuses are described in EP 1 790 958 A1, WO 02/02168 A1, EP 0 937 004 B2 and EP 0 789 230 B1.
Proceeding from the above-mentioned prior art, the invention is based on the problem of indicating a powder metering apparatus constructed as simply as possible for the exact volume metering of pulverulent substances, in which the powder metering volume is able to be set in a simple manner and/or in which emptying problems are reliably prevented.
The object consists in addition in indicating a correspondingly improved method for operating a powder metering apparatus.